1. Field of the Invention
The invention relates to an underframe for a rail-borne vehicle, more specifically a rail-borne crane, for transporting freely movable loads having a plurality of curve-negotiating wheel sets which are accommodated in bogies and mounted in one or more running-gear frames for rolling on the running rails.
2. Description of the Related Art
In general, rail-borne vehicles are distinguished by the fact that they can be transported quickly and simply on rails to their places of use where they are then maneuverable Win a freely movable manner even with suspended load. Vehicles of this type include, for example, railroad cranes which are used in track laying, bridge construction, and as breakdown cranes. Railroad cranes are required to be transportable quickly on the rails to the place of use and must often be able to maneuver large loads in a very confined space.
Rail-borne cranes or other rail-borne vehicles with high working loads require a correspondingly large number of wheel sets so that the dead weight of the vehicle and the working load may be transferred to the rails without overloading the individual contact points of the wheels with the rails. The conventional wheel sets of the rail-borne crane must be arranged in pairs on bogies so that the rail-borne vehicle is capable of negotiating curves. Accordingly, the use of a large number of conventional wheel sets is not only expensive and increases the overall vehicle length, but also increase the unladen weight of the vehicle. The unladen weight of the vehicle, however, cannot be indefinitely increased as desired, for limits are set by the specifications of the operators of the railroad network and by the loading capacity of the running rails and of the subsoil. The working load which is added to the dead weight of the vehicle is thus also limited by the same constraints. Every increase in the dead weight of the vehicle ultimately means a reduction in the working load capacity.
Attempts therefore have to be made to keep the dead weight of the vehicle as low as possible in favor of the working load. German Patent 196 54 521, for example, proposes to split up the vehicle frame, extending over the entire vehicle length, and thereby make it lighter. However, making the vehicle frame lighter may have an adverse effect on the stability. Therefore, other ways have to be sought to increase the lifting capacity of the vehicle of the generic type.
The object of the present invention is to provide an underframe for a rail-borne vehicle for transporting freely movable loads which achieves high working loads with good maneuverability of the vehicle without greatly increasing the dead weight of the vehicle and is simultaneously cost-effectively manufactured.
The object according to the present invention is met by relieving the load on the conventional wheel sets of the vehicle with at least one supporting-wheel set consisting of two supporting wheels. The supporting-wheel set is fastened to the vehicle so so that it can be raised to a rest position above the rail and lowered from the rest position into an operative position in which each supporting wheel rests with adjustable pressure on one of the rails.
It was hitherto possible to increase the freely movable working loads of a vehicle of the generic type by increasing the amount of conventional wheel sets with a correspondingly high dead weight and extension of the entire vehicle. The increase in the working load is made possible by the present invention without extending the length of the underframe because the supporting-wheel sets relieve the permenent wheel sets of load during the load application, i.e., when a load is supported by the vehicle. The supporting wheels of the supporting-wheel set or the supporting-wheel sets are lowered onto the rails in a simple manner and absorb some of the working load, for which a separate twin wheel set would otherwise have been necessary. During the rail transport of the rail-borne vehicle, the supporting-wheel set is raised and the vehicle moves on the conventional wheel sets and may be taken to the place of use at high transport speeds. The degree of load relief of the conventional wheel sets at the place of use may be determined by setting the bearing pressure of the supporting-wheel set on the rail between 0 and a maximum (for example 17 t). Furthermore, a corresponding control may be provided so that the percentage of the load to be absorbed by the supporting-wheel set is maintained.
The supporting-wheel set may be arranged on the running-gear frame directly adjacent to one of the conventional wheel sets, the supporting wheels preferably having a smaller diameter than the wheels of the conventional wheel sets. The use of smaller wheels saves weight and space for accommodating the supporting-wheel sets, of which preferably at least two are provided on both sides of the vehicle.
According to an embodiment of the present invention, the supporting-wheel set is arranged between the conventional wheel sets of the underframe. A suitable solution is to arrange the supporting-wheel set in the region below the pivot of the bogie, since the load relief of the wheel sets is at its most effective there.
In a refined embodiment according to the present invention, the supporting wheel set is arranged on a link and may be raised and lowered hydraulically or hydropneumatically. Appropriate pressure-medium cylinders are arranged between the link and the underframe proximate the supporting wheels, the supply of pressure medium being effected in a pressure-controlled manner to set the supporting load of the supporting-wheel set.
According to a further embodiment of the invention, the wheel pressures of the supporting-wheel set are separately adjustable on each side of the vehicle. The separate adjustability of the supporting wheels on opposite side of the vehice allows controlling each wheel according to loads individually recorded during the maneuvering of the load.
In another embodiment of the present invention, the supporting wheels of each supporting-wheel set may be arranged individually on wheel-guide levers which are then in turn connected to the pressure-medium cylinders of the hydraulic system or hydropneumatic system.
To compensate for differences in radii of each wheel set when passing through curved sections, the supporting wheels of each supporting-wheel set may be mounted so as to be displaceable in the axial direction.
In an alternative embodiment, the supporting wheels may be driven for providing mobile assistance when moving the vehicle under load.
The present invention provides an under frame with high lifting capacities that is short and cost-effective. The high lifting capacity is achieved with simple means which enable the forces which act on the conventional wheel sets from the working load to be distributed over at least one additional supporting-wheel set when the vehicle is moving under load to either relieve the load on the conventional wheel sets of the vehicle or to increase the lifting capacity of the vehicle. The supporting wheels may of course also be arranged in a larger number at suitable points of the underframe. The measures are simple and save weight compared with the additional of further conventional wheel sets so that a favorable solution is obtained for the crane operator.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.